The present application claims the right of priority under 35 U.S.C. xc2xa7119(a) based on German Patent Application No. 100 61 545.7, filed Dec. 11, 2000, the entire content of which is hereby incorporated by reference.
The present invention relates to a method of monitoring refrigerant level (filling amount of refrigerant) in a refrigerant circuit of an air-conditioning or heat-pump system with a compressor and a refrigerant operated in the supercritical range as a function of the operating point.
In this case, a xe2x80x9crefrigerant which may, depending on the operating point, be operated in the supercritical rangexe2x80x9d is to be understood as one which, at least for some of the possible system operating states, is in the supercritical range and is therefore present in vapor form even in the section of the refrigerant circuit from the xe2x80x9ccondenserxe2x80x9d, (functioning at such time as a gas cooler) to the evaporator. In particular, the method is suitable for monitoring the CO2 level in CO2 air-conditioning systems, which are increasingly being used in motor vehicles. The method includes standstill level monitoring, that is to say level monitoring with the compressor switched off, and/or in-operation level monitoring, that is to say level monitoring with the compressor switched on.
U.S. Pat. No. 4,745,765 includes in-operation level monitoring in which conclusions are drawn about possible underfilling, by using the measured temperature of superheated refrigerant at the evaporator output and the ambient temperature.
U.S. Pat. No. 5,481,884 describes a method which includes both standstill and in-operation level monitoring. To this end, when the air-conditioning or heat-pump system considered there is at a standstill, the refrigerant pressure on the suction side of the compressor and the ambient temperature are measured. The saturation pressure associated with the measured ambient temperature is determined and used as a reference pressure, with which the measured refrigerant pressure is compared. If the measured pressure compared with the reference pressure is too low, it is concluded that there is underfilling. During operation of the system, temperature and pressure of the refrigerant are measured on the suction side of the compressor. The saturation temperature associated with the measured pressure is determined and used as a reference temperature, with which the measured refrigerant temperature is compared. If the measured temperature lies too far above the reference temperature, it is concluded that there is underfilling.
The present invention has as its principal object to provide a novel method of refrigerant level monitoring of the general type mentioned above. With relatively little effort, the method permits reliable detection of erroneous filling, i.e., both underfilling and/or overfilling, on a refrigerant which may, depending on the operating point, be operated in the supercritical range in a refrigerant circuit of an air-conditioning or heat-pump system.
In accomplishing the objects of the invention, there has been provided according to one aspect a method of refrigerant level monitoring in a refrigerant circuit of an air-conditioning or heat-pump system having a compressor and a refrigerant which may, depending on of the operating point, be operated in the supercritical range, the method comprising: at least standstill level monitoring with the compressor switched off, comprising measuring both the pressure (pKM) and the temperature (TKM) of the refrigerant, and determining whether the measured refrigerant pressure lies below a temperature-independent predetermined minimum pressure value (pmin) or whether the measured refrigerant temperature lies above a predetermined maximum saturation temperature value (TS) and the measured refrigerant pressure lies outside a predetermined target pressure range (pu, po).
In a preferred embodiment, the method further comprises in-operation level monitoring with the compressor switched on, which is carried out by measuring the refrigerant superheat (dTxc3xc) at the evaporator of the system, and determining whether the measured superheat (dTxc3xc) lies above a predetermined limiting value (dTxc3xcG).
According to another preferred embodiment of the invention, there has been provided a method of refrigerant level monitoring in a refrigerant circuit of an air-conditioning or heat-pump system having a compressor and a refrigerant which may, depending on the operating point, be operated in the supercritical range, the method comprising: at least in-operation level monitoring with the compressor switched on, comprising measuring the refrigerant superheat (dTxc3xc) at the evaporator of the system, and determining whether the measured superheat (dTxc3xc) lies above a predetermined limiting value (dTxc3xcG).
According to another aspect of the invention, there has been provided an apparatus for refrigerant level monitoring in a refrigerant circuit of an air-conditioning or heat-pump system having a compressor and a refrigerant which may, depending on the operating point, be operated in the supercritical range, the apparatus comprising: at least a system for standstill level monitoring with the compressor switched off, comprising detectors for measuring both the pressure (pKM) and the temperature (TKM) of the refrigerant, and a calculation circuit for determining whether the measured refrigerant pressure lies below a temperature-independent predetermined minimum pressure value (pmin) or whether the measured refrigerant temperature lies above a predetermined maximum saturation temperature value (TS) and the measured refrigerant pressure lies outside a predetermined target pressure range (pu, po).
According to another preferred embodiment, the apparatus comprises, either as an alternative or in addition to the system for standstill level monitoring, a system for in-operation level monitoring with the compressor switched on, comprising detectors for measuring the refrigerant superheat (dTxc3xc) at the evaporator of the system, and a calculation circuit for determining whether the measured superheat (dTxc3xc) lies above a predetermined limiting value (dTxc3xcG).
According to yet another aspect of the invention, there has been provided a motor vehicle embodying the apparatus described above in an air-conditioning system that employs CO2 as refrigerant.
Further objects, features and advantages of the present invention will become apparent from the detailed description of preferred embodiments that follows, when considered together with the accompanying figures of drawing.